Photolithography is often a critical step in the fabrication of semiconductor devices, and has become more complicated due to the rapidly-shrinking dimensions of the semiconductor devices. In a photolithographic process, the accuracy and reliability of a patterned photoresist (PR) layer plays an important role in device performance. For example, when a patterned PR layer is found to have defects (e.g., from misalignment, from over-etching, and/or remnants on the surface of patterned PR layer), instead of proceeding to an etching process, a manufacturer would normally have the patterned PR layer reworked to prevent permanent damage to the entire batch of chips in subsequent processes.
Generally, a multi-layer (photo-) resist process can be used to improve photolithographic pattern transfer performance. For example, the multi-layer resist process can be a tri-layer resist process including a tri-layer resist (TLR) stack that has, for example, a PR layer on a SOG (spin-on glass) layer on an under-layer. One conventional method for resist reworking includes removing the incorrectly developed PR layer from the silicon chip by solvents (e.g., chemical wet etching). Since the incorrect PR layer has already been cured and bombarded, solvent rework often leaves residues and results in changes of SOG thickness, resist footing behavior, and/or refractive indices. In addition, solvent rework can be used to remove only the resist layer in a single process. Another conventional method for resist reworking can include an ash rework, which can be used to remove the PR layer and/or the under-layer (UL) but cannot remove the SOG layer of the tri-layer resist stack. Consequently, the solvent and/or ash rework process can only be used to remove a certain portion of the tri-layer resist stack in a single process. Therefore, multiple processing steps on multiple tools may be needed in order to remove, e.g., a full TLR stack.
Thus, there is a need to overcome these and other problems of the prior art and to provide a flexible technique for resist reworking by removing any desired portions of the tri-layer resist stack in a single process.